The present invention relates to a magnetoresistance element whose electrical resistance changes depending on the magnetic field, a manufacturing method of the magnetoresistance element, a magnetic field detection system employing the magnetoresistance element, and a magnetic recording system employing the magnetic field detection system.
Magnetoresistance elements or magnetoresistance sensors have been used for heads of HDDs (Hard Disk Drives) of computers, and the magnetoresistance element realizes readout of information which has been stored in a high-density record medium. The magnetoresistance element (magnetoresistance head) changes its electrical resistance depending on the intensity and direction of the magnetic field around it. Therefore, if a constant voltage is applied to the magnetoresistance head, current passing through the magnetoresistance head changes as the magnetic field changes (as the position of the magnetoresistance head in relation to the record medium changes), thereby the information which has been stored in the record medium can be read out as a current signal.
Concretely, the magnetoresistance element basically behaves based on the AMR (Anisotropic MagnetoResistance) effect. In the case of the AMR effect, a component of an electrical resistance vector can be expressed as:
R=Axc2x7cos2 xcex8
where xcex8 is the angle between the direction of magnetization of the magnetoresistance element and the direction of a sense current passing through the magnetoresistance element. With regard to the AMR effect, a detailed description has been given in a document: D. A. Thompson et al. xe2x80x9cMemory, Storage and Related Applicationsxe2x80x9d, IEEE Trans. on Mag. MAG-11, Page 1039 (1975).
In a magnetoresistance sensor employing the AMR effect, the so-called Barkhausen noise occurs. In order to reduce the Barkhausen noise, a longitudinal bias magnetic field is generally applied to the magnetoresistance sensor. The application of the longitudinal bias magnetic field is usually implemented by antiferromagnetic material such as FeMn, NiMn, Ni oxide, etc. Incidentally, the xe2x80x9cFeMnxe2x80x9d and xe2x80x9cNiMnxe2x80x9d are chemical symbols, and hereafter, such chemical symbols will be used for the sake of brevity of expression.
In recent years, new types of magnetoresistance effects which are called xe2x80x9cgiant magnetoresistance effectxe2x80x9d, xe2x80x9cspin valve effectxe2x80x9d, etc. have been reported and have attracted considerable attention. Such effects, which are stronger than the conventional AMR effect, can be observed in an artificial lattice which is composed of ferromagnetic layers and non-magnetic conduction layers which are stacked alternately. The behavior of electrical resistance of such an artificial lattice has been explained from the viewpoint of spin-dependent transfer of conduction electrons between the ferromagnetic layers through the non-magnetic conduction layers, or spin-dependent scattering of the conduction electrons at the interfaces between the layers. In a magnetoresistance sensor composed of such an artificial lattice, an in-plane resistance of a pair of ferromagnetic layers separated by a non-magnetic conduction layer changes as:
R=Bxc2x7cos xcfx86
where xcfx86 is the angle between magnetization directions of the two ferromagnetic layers. The magnetoresistance sensor employing the giant magnetoresistance effect of such an artificial lattice is more highly sensitive (larger xcex94R) than the magnetoresistance sensors employing the AMR effect.
In Japanese Patent Application Laid-Open No.HEI2-61572 (Japanese Gazette Containing the Patent No.2651015), a layered magnetic structure which exhibits a large magnetoresistance effect due to anti-parallel magnetization directions between magnetic layers has been disclosed. The layered structure is composed of a first permalloy layer, a second permalloy layer, an interlayer between the two permalloy layers, and a pinning (fixing) layer below the second permalloy layer. The two permalloy layers having opposite magnetization directions are separated by the interlayer (5 nm Au layer, for example), and the magnetization of the second permalloy layer is pinned (fixed) by the pinning layer which is preferably implemented by an FeMn layer.
In Japanese Patent Application Laid-Open No.HEI4-358310 (Japanese Publication of Examined Patent Applications No.HEI8-21166) and Japanese Patent Application Laid-Open No.HEI6-203340 (Japanese Gazette Containing the Patent No.2725987), a layered magnetic structure named xe2x80x9cspin valvexe2x80x9d has been disclosed. The layered magnetic structure includes a first ferromagnetic layer (soft), a second ferromagnetic layer and a non-magnetic metal layer which separates the two ferromagnetic layers. The angle between the magnetization directions of the two ferromagnetic layers is 90 degrees when a magnetic field applied thereto is 0, and the in-plane electrical resistance of the non-coupled two ferromagnetic layers separated by the non-magnetic metal layer changes proportionally to the aforementioned xe2x80x9ccos xcfx86xe2x80x9d (where xcfx86 is the angle between magnetization directions of the two ferromagnetic layers), independently of the direction of the sense current passing through the pin valve magnetoresistance sensor.
A magnetoresistance sensor employing a ferromagnetic tunnel junction has been disclosed in Japanese Patent Application Laid-Open No.HEI10-162327.
FIG. 1 is a vertical sectional view showing an example of a conventional magnetoresistance element which is employed as a magnetoresistance sensor. FIG. 2 is a plan view showing a lower electrode layer and an upper electrode layer of the conventional magnetoresistance element of FIG. 1. Incidentally, FIG. 1 is showing a vertical section taken along the line C-Cxe2x80x2 shown in FIG. 2. In the magnetoresistance element 102 shown in FIGS. 1 and 2, a lower gap layer 106 is formed on a lower shield layer 104 which is formed on an unshown substrate, and a lower electrode layer 108 is formed on the lower gap layer 106. A magnetoresistance effect layer 110 is formed on the lower electrode layer 108, and a upper electrode layer 112 is formed on the magnetoresistance effect layer 110. The upper electrode layer 112 is composed of a first upper electrode layer 114 and a second upper electrode layer 116. The first upper electrode layer 114 is formed directly on the magnetoresistance effect layer 110 so as to cover the magnetoresistance effect layer 110, and the second upper electrode layer 116 is formed on the first upper electrode layer 114. An upper gap layer 113 is formed on the upper electrode layer 112, and an upper shield layer 115 is formed on the upper gap layer 113.
The flat surface 118 on the left-hand end of the structure shown in FIG. 1 is the so-called ABS (Air Bearing Surface). When information stored in a magnetic recording medium is read out by the magnetoresistance element 102, the magnetoresistance element 102 is positioned so that the ABS 118 will face the surface of the magnetic recording medium and a narrow gap will be formed between the ABS 118 and the surface.
In the manufacturing process of the magnetoresistance element 102, the lower electrode layer 108 is generally formed by the following process (1) or (2).
(1) An electrode layer to be formed as the lower electrode layer 108 is deposited on the entire surface of the lower gap layer 106, and a photoresist layer (pattern) is formed on the electrode layer. Subsequently, unnecessary part of the electrode layer is removed by means of milling so that the lower electrode layer 108 will be patterned to a predetermined shape. Thereafter, the photoresist layer remaining on the patterned lower electrode layer 108 is removed by use of a release agent.
(2) A photoresist layer for lift-off is formed on part of the surface of the lower gap layer 106, and an electrode layer to be formed as the lower electrode layer 108 is deposited on the photoresist layer and the lower gap layer 106. Thereafter, the photoresist layer is removed by use of a release agent (lift-off).
FIG. 3 is a vertical sectional view showing a stage in the above process (1) just after the step for patterning the lower electrode layer 108. After the patterning step, the photoresist layer 120 remaining on the patterned lower electrode layer 108 is removed by use of a release agent.
However, in the above photoresist layer removing step, the edge 122 of the lower electrode layer 108 is exposed to the release agent in which the photoresist has been dissolved, thereby the edge 122 of the lower electrode layer 108 is eroded or flakes off due to the release agent containing the dissolved photoresist. Consequently, there are cases where the roughness of the edge 122 of the lower electrode layer 108 is increased to as large as hundreds of nanometers.
Also in the case of the process (2), when the photoresist for lift-off is removed by use of the release agent, the edge 122 of the lower electrode layer 108 is similarly exposed to the release agent containing the dissolved photoresist, thereby the same problem as that of the process (1) occurs.
As seen in FIGS. 1 and 2, above the edge 122 of the lower electrode layer 108, the second upper electrode layer 116 (which is formed on an insulation layer 124) spreads. If the roughness of the lower electrode layer edge 122 enlarges as above, an electrical short circuit between the lower electrode layer edge 122 and the second upper electrode layer 116 tends to occur and such shorts have actually been reported. The shorts seem to occurs due to curling-up of part of the lower electrode layer 108 near the edge 122, materials of the eroded/flaked lower electrode layer edge 122 which redeposited on the edge 122, etc. Due to such a short circuit, even if a sense current is passed between the upper electrode layer 112 and the lower electrode layer 108, the sense current passes through the short circuit between the electrode layers without passing through the magnetoresistance effect layer 110, thereby the detection of the magnetic field by the change of the resistance of the magnetoresistance effect layer 110 becomes difficult. Consequently, the sensitivity and performance of the magnetoresistance elements 102 manufactured by the above processes are necessitated to be deteriorated, or manufacturing yield of the magnetoresistance elements 102 is necessitated to be decreased, causing higher cost.
It is therefore the primary object of the present invention to provide a magnetoresistance element having a structure in which the shorts between the upper electrode layer and the lower electrode layer is prevented.
Another object of the present invention is to provide a manufacturing method of a magnetoresistance element by which the shorts between the upper electrode layer and the lower electrode layer of the magnetoresistance element is prevented.
Another object of the present invention is to provide a magnetoresistance magnetic field detection system (a magnetic field detection system employing a magnetoresistance element) in which the shorts between the upper electrode layer and the lower electrode layer of the magnetoresistance element is prevented and thereby high performance and low cost of the system are realized.
Another object of the present invention is to provide a magnetic recording system employing a magnetoresistance element in which the shorts between the upper electrode layer and the lower electrode layer of the magnetoresistance element is prevented and thereby high performance and low cost of the system are realized.
In accordance with a first aspect of the present invention, there is provided a magnetoresistance element comprising a lower electrode layer, a magnetoresistance effect layer and an upper electrode layer. The lower electrode layer is formed directly on a lower shield layer or on another layer which is formed on the lower shield layer or so as to serve also as the lower shield layer. The magnetoresistance effect layer is formed on part of the upper surface of the lower electrode layer. The upper electrode layer is formed above the lower electrode layer so that part of its lower surface will at least be in contact with the upper surface of the magnetoresistance effect layer and so that the upper electrode layer seen in a plan view will avoid the edge of the lower electrode layer except at the ABS (Air Bearing Surface) of the magnetoresistance element.
In accordance with a second aspect of the present invention, the edge of the upper electrode layer facing the ABS forms part of the ABS.
In accordance with a third aspect of the present invention, the edge of the upper electrode layer facing the ABS is formed withdrawn from the ABS.
In accordance with a fourth aspect of the present invention, the upper electrode layer includes a first upper electrode layer and a second upper electrode layer. The first upper electrode layer is formed on the magnetoresistance effect layer in almost the same area as that of the magnetoresistance effect layer. The second upper electrode layer is formed above the lower electrode layer so that part of the lower surface of the second upper electrode layer will be in contact with the upper surface of the first upper electrode layer.
In accordance with a fifth aspect of the present invention, an insulation layer is formed between the lower electrode layer and the second upper electrode layer.
In accordance with a sixth aspect of the present invention, the lower shield layer is formed on a substrate, and the lower electrode layer is formed on part of the upper surface of the lower shield layer.
In accordance with a seventh aspect of the present invention, the lower electrode layer also serves as the lower shield layer.
In accordance with an eighth aspect of the present invention, the lower shield layer is formed on a substrate, and a lower gap layer is formed on the lower shield layer, and the lower electrode layer is formed on part of the upper surface of the lower gap layer.
In accordance with a ninth aspect of the present invention, the magnetoresistance element further comprises an upper shield layer which is formed on the upper electrode layer.
In accordance with a tenth aspect of the present invention, the upper electrode layer also serves as an upper shield layer.
In accordance with an eleventh aspect of the present invention, the magnetoresistance element further comprises an upper gap layer which is formed on the upper electrode layer, and an upper shield layer which is formed on the upper gap layer.
In accordance with a twelfth aspect of the present invention, the magnetoresistance element further comprises a longitudinal bias layer which is formed nearby or in contact with the magnetoresistance effect layer for applying a longitudinal basis magnetic field to the magnetoresistance effect layer.
In accordance with a thirteenth aspect of the present invention, the longitudinal bias layer is formed on the upper surface of the lower electrode layer on both sides of the magnetoresistance effect layer.
In accordance with a fourteenth aspect of the present invention, the longitudinal bias layer is formed so that its part will at least be in contact with the magnetoresistance effect layer.
In accordance with a fifteenth aspect of the present invention, the magnetoresistance effect layer is composed of ferromagnetic tunnel junction layers.
In accordance with a sixteenth aspect of the present invention, the magnetoresistance effect layer includes a free layer which is formed over the lower electrode layer, a non-magnetic layer which is formed over the free layer, a pinned layer which is formed over the non-magnetic layer, and a pinning layer which is formed over the pinned layer for pinning the direction of magnetization of the pinned layer.
In accordance with a seventeenth aspect of the present invention, the magnetoresistance effect layer includes a free layer which is formed under the upper electrode layer, a non-magnetic layer which is formed under the free layer, a pinned layer which is formed under the non-magnetic layer, and a pinning layer which is formed under the pinned layer for pinning the direction of magnetization of the pinned layer.
In accordance with a eighteenth aspect of the present invention, there is provided a manufacturing method of a magnetoresistance element which is provided with a lower electrode layer which is formed directly on a lower shield layer or on another layer which is formed on the lower shield layer or so as to serve also as the lower shield layer, a magnetoresistance effect layer which is formed on part of the upper surface of the lower electrode layer, and an upper electrode layer which is formed above the lower electrode layer so that part of its lower surface will at least be in contact with the upper surface of the magnetoresistance effect layer. In the manufacturing method, an insulation layer is formed around the magnetoresistance effect layer which is formed on the lower electrode layer, and the upper electrode layer is formed and patterned on the magnetoresistance effect layer and the insulation layer by use of a photoresist so that the upper electrode layer seen in a plan view will avoid the edge of the lower electrode layer except at the ABS (Air Bearing Surface) of the magnetoresistance element.
In accordance with a nineteenth aspect of the present invention, the patterning of the upper electrode layer by use of the photoresist is conducted by milling or lift-off.
In accordance with a twentieth aspect of the present invention, there is provided a magnetic field detection system comprising a magnetoresistance element, a current passage means and a resistivity detection means. The a magnetoresistance element includes a lower electrode layer which is formed directly on a lower shield layer or on another layer which is formed on the lower shield layer or so as to serve also as the lower shield layer, a magnetoresistance effect layer which is formed on part of the upper surface of the lower electrode layer, and an upper electrode layer which is formed above the lower electrode layer so that part of its lower surface will at least be in contact with the upper surface of the magnetoresistance effect layer and so that the upper electrode layer seen in a plan view will avoid the edge of the lower electrode layer except at the ABS (Air Bearing Surface) of the magnetoresistance element. The current passage means passes a sense current between the upper electrode layer and the lower electrode layer of the magnetoresistance element. The resistivity detection means detects the change of resistivity of the magnetoresistance element based on the sense current passed by the current passage means between the upper electrode layer and the lower electrode layer.
In accordance with a twenty-first aspect of the present invention, there is provided a magnetic recording system comprising a reproduction head, a current passage means, a resistivity detection means and a driving means. The reproduction head employs a magnetoresistance element including a lower electrode layer which is formed directly on a lower shield layer or on another layer which is formed on the lower shield layer or so as to serve also as the lower shield layer, a magnetoresistance effect layer which is formed on part of the upper surface of the lower electrode layer, and an upper electrode layer which is formed above the lower electrode layer so that part of its lower surface will at least be in contact with the upper surface of the magnetoresistance effect layer and so that the upper electrode layer seen in a plan view will avoid the edge of the lower electrode layer except at the ABS (Air Bearing Surface) of the magnetoresistance element. The current passage means passes a sense current between the upper electrode layer and the lower electrode layer of the magnetoresistance element of the reproduction head. The resistivity detection means detects the change of resistivity of the magnetoresistance element based on the sense current passed by the current passage means between the upper electrode layer and the lower electrode layer. The driving means drives the reproduction head and places the magnetoresistance element of the reproduction head on a selected track of an information storage surface of a magnetic recording medium.
In accordance with a twenty-second aspect of the present invention, the magnetic recording system further comprises a recording head which is attached to the reproduction head so as to be driven by the driving means together with the reproduction head and placed on a selected track of the information storage surface of the magnetic recording medium.